Many fluids with varying contaminant levels, such as encountered in batch processing, are processed by passing them though filtration media. The producers of beer and wine, for example, typically subject their products to filtration during processing in order to provide such products with an acceptable level of purity. Economics dictate that devices used to conduct such filtration not only provide a product with the desired purity, but that they do so at a commercially feasible rate. As such, most mass producers of beer and wine employ a large number of filters which are integrated so as to form a filtration system. By way of example, a typical system for filtering beer may incorporate about 320 individual filter cartridges connected in parallel to a common feed stream of contaminated beer. Each such cartridge in the system, which comprises one or more pleated, microporous nylon or polyvinylidene fluoride membranes within a plastic or metal housing, is designed to filter about 50-100 gallons of liquid per minute.
When a fluid is being filtered by such a filtration system, the pressure drop across each filter is initially generally stable and remains generally invariant at that level for a substantial period of time. As passage of the liquid through the filter continues, however, the pressure drop across the filter rapidly increases as a result of the build-up of contaminants, e.g., bacteria and particulate matter, on the filter. At some point, the pressure drop becomes so great that the filter must be replaced. While such contaminant-loaded filters may be regenerated by backflushing and thereafter reused, it is generally recognized that once a filter has reached the condition where the pressure drop across the filter has increased over the previously described initial level, even by only about 1 or 2 psi, such backflushing will not completely remove the contaminants so as to restore the initial pressure drop across the filter. This incomplete contaminant removal is undesirable inasmuch as such backwashed filters, possessing a lower overall contaminant loading capacity, must be changed on an increasingly more frequent basis as compared to new or completely contaminant-free filters. This results in higher production costs due to increased system down-time.
It has been recognized, however, that substantially complete removal of contaminants from a filter can be achieved if backflushing is completed on a filter which has not experienced the aforesaid increase in pressure drop from its initial, stable level. Due to the rapidity of the pressure drop increase once the pressure drop begins to increase above the generally invariant initial level, it has been difficult to monitor the pressure drop and stop the filtration process immediately preceding the pressure drop increase. In view of these factors, operators of such systems typically estimate the time it will take for the pressure drop across the filters to increase above their initial levels, such estimates being based purely upon the prior personal experience of the operator in using identical filters. Using this information, and in order to provide an adequate level of safety, an operator will typically replace the filters after they have been in use about 50%, and possibly as high as 70%, of the total time the operator believes it will take for the pressure drop across the filters to increase from their initial level.
Certain inefficiencies, however, arise when using the aforesaid estimating method. One of these inefficiencies is that the filters are replaced prematurely, resulting in unnecessary down-time and increased production costs. Further problems are introduced when one desires to filter beer and wine, or other products, prepared by batch production methods. For example, in the case of beer and wine, the level of contaminant loading of each batch, despite the efforts of its producer, will not only vary from batch to batch, but is difficult to determine with precision in a commercial setting. As filters typically used in such filtration systems possess sufficient capacity (even when replaced prematurely as described previously) to filter more than one batch of beer or wine before requiring replacement, the uncertain level of contaminant loading of each batch, combined with the variation in such loading from batch to batch, introduces further uncertainty and potential error into the aforesaid estimation method. In such filtration systems, the operator will tend to be even more conservative as to deciding when the filters should be cycled, thereby introducing a further degree of inefficiency into the filtration process.
Accordingly, there exists a need for a method which provides for the operation of a filtration system involving the cycling of filters in a manner which is more efficient than known methods. Further, the method should be operable regardless of any variation in, or knowledge of, the degree of contamination of the fluid to be filtered. These and other objects and advantages of the present invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.